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9.4 Information systems 6. Optical fibre communication systems
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Syllabus reference (October 2002 version) |
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| 6. Electrical energy can be converted to light energy for use in optical fibre communication systems |
Students learn to: |
Students: |
Extract from Senior Science Stage 6 Syllabus (Amended October 2002). Board of Studies, NSW.
[Edit: 28 Aug 08]
Prior learning: Science Stages 4-5, Outcome 5.6 (content 5.6.4: light energy).
perform a first-hand investigation to demonstrate the transmission of light through an optic fibre
- For this syllabus requirement, the use of a 40 Watt lamp or a strong torch is quite adequate. A ray box kit would also be useful. Familiarise yourself with the safety precautions to be observed with whatever equipment you use. Be particularly mindful of the safety precautions to be followed if you use a laser for any of your experiments.
- While performing the investigation, consider how far you can bend the light from its original path using different materials. Observe any losses of light when comparing materials. You can efficiently compare the different materials by constructing a data table to record your observations.
- You can use a variety of materials, such as different plastic tubes, optic fibre cable of different grades and a stream of water. Using a soft drink bottle that has a small hole placed in the centre can produce a stream of water. Fill the bottle, covering the hole and replacing the lid. Aim a light source behind the hole so that the beam passes through the bottle to the hole. Remove the lid to produce a stream of water. Observe light internally reflecting through the stream.
outline properties of optical fibres as communication carriers
Background
Optical fibres are long, thin, transparent strands of glass. They are used to transmit pulses of light generated by a laser. A typical optical fibre consists of a very pure glass core surrounded by a cladding of low refractive index.
- The glass in optical fibres is made so that light is unable to emerge side ways from the glass. This is achieved by covering the glass with a cladding of denser glass or plastic. As light travels from the inner glass core to the denser cladding, it bends so much that, instead of leaving the glass, it is reflected back into it. This process is known as total internal reflection.
More information on optical fibre 
Wikipedia .
outline the principle of total internal reflection and relate this to the advantages of fibre optics over more conventional carriers of information
- Total internal reflection occurs when light travelling from a more-dense to a less-dense medium hits the boundary between them. Some degree of reflection back into the denser medium (internal reflection) always accompanies refraction. When the angle of incidence is greater than the critical angle, total internal reflection occurs, i.e. all the light is internally reflected.
- Optical fibres, using laser generated light, can transmit many more messages at one time than coaxial cable or microwaves. The pulses of light are produced millions of times per second and pass along the optical fibre being reflected from the walls several thousand times per metre.
- Glass and plastic fibres as thin as a few micrometres in diameter can be used to transmit light with very little loss of intensity. Even if the fibres are bent the critical angle is rarely exceeded and the signal will be transmitted.
Total internal reflection University of Winnipeg, Canada
process and analyse information from
secondary sources to compare and contrast copper cables with fibre
optic cables in relation to:
- carrying capacity
- cost
- rate of information transfer
- security
Some suggestions:
A good way to compare and contrast is to construct a table and record the information in a concise form.
Use comparable units when data is supplied to make comparisons easier.
As well as the usual sources of information, see if you can contact local suppliers of cables.
- Process your information by identifying the comparative criteria in each of your sources.
- Analyse the information provided, selecting numerical values and qualitative descriptions and interpreting their meaning.
Guidelines for using fiber optic cable Black Box Explains...Guidelines for choosing fibre optic cable, Black Box Network Services, USA
This site has some excellent information on the comparison between fibre optics and copper.
New Fibre-Optic Connections Overtake Cable
IT News, Haymarket, Australia, 2008
Modern communication: the laser and fibre optic revolution
US National Academy of Sciences, Washington DC. USA, 2003
outline the differences and the relative merits in the use of fibre optic cables and metal cables to transmit and receive information
- Fibre optic cables have the following advantages when compared to wire based (or radio wave based) systems:
- have a much greater bandwidth than metal cables. This means that they can carry more data per second, e.g. can transmit several gigabytes of data per second.
- are not affected by radio waves, so there is no static
- are much thinner and lighter than metal wires
- are less susceptible to corrosion than metal cables
- can handle digitally coded light (the natural form for computer data), as well as analog signals
- can multiplex thousands of voice channels together over a single optical fibre
- more secure as information cannot be intercepted easily.
- The main disadvantage of fibre optics is that the cables are expensive to install. In addition, they are more fragile than wire and must be spliced together precisely and carefully.
- Repeaters need to be added every 55-65 kilometres to boost the signal strength.
- A fibre optic system is a particularly popular technology for local area networks. In addition, telephone companies are steadily replacing traditional metallic telephone lines with fibre optic cables.
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